多载波码分多址在低密度二分图上的建模与分析

Modeling and analysis of multicarrier code division multiple access upon Tanner graph

多载波码分多址是移动通信重要的多址技术之一,传统方法将扩频序列的构造和多用户检测单独考虑,未能做到发射机和接收机的一体化设计。受到低密度奇偶校验码的启发,基于图论建立多载波码分多址收发机模型,采用二分图定义码片和数据符号间的扩频关系。在此基础上,利用适合低密度二分图的消息传递算法完成多用户迭代检测,推导并分析洪水消息传递和串行消息传递两种检测机制。仿真结果表明,当传统的多载波码分多址系统陷入严重过载而不能正常通信的情况下,基于低密度二分图的多载波码分多址系统依然能够达到理想的传输性能,为下一代移动通信系统的设计提供了有益的参考。

MC-CDMA（ multicarrier-code division multiple access） is an important multiple access technique for mobile communications. In conventional MC-CDMA,construction of spreading sequences and multiuser detection are considered separately,which means that the transmitter and the receiver are not designed jointly. Inspired by LDPC（ low density parity check） codes,the transceiver models of MC-CDMA based on graph theory were designed,and the low density Tanner graph was used to describe the relationship between spreading chips and data symbols. In addition,message passing algorithm,which was suitable for the Tanner graph,was utilized to perform iterative multiuser detection. Flooding and serial schedules for the message passing were deduced and analyzed. Simulation results show that the conventional MC-CDMA cannot perform well under the overloading conditions,while the proposed low density Tanner graph for MC-CDMA achieves satisfactory performance,which provides the useful reference for the design of next generation mobile networks.